The present invention relates generally to the design and construction of a bladed rotor disk for use in a gas turbine engine. More particularly, the present invention has one application wherein a pair of high specific strength remote support rings are utilized to support the blade carrying member of the rotor disk and resist a centrifugal load generated by the rotating components. Although the invention was developed for use in a gas turbine engine, certain applications may be outside of this field.
It is well known that a gas turbine engine integrates a compressor and a turbine having components that rotate at extremely high speeds. Typically, the rotating components within a gas turbine engine include a rotor disk having a plurality of circumferentially spaced blades which extend radially outward from the rotor disk. During operation of the gas turbine engine the rotor disk and blades are rotated, therefore a centrifugal force attendant with rotation acts on the components in a radial direction.
A conventional rotor disk includes an outer rim and an inner hub with a radially extending web therebetween. The outer rim has an axial width sufficient to ensure low stress therein when subjected to centrifugal loading or forces imposed by the rotating components. Generally, the radially extending web has an axial width smaller than that of the outer rim in order to minimize the weight of the rotor disk, and the axial width of the inner hub has about the same axial width as the outer rim in order to provide needed structural integrity for the rotor disk.
The rotor disk of a gas turbine engine typically has relatively high rotation energy related to the centrifugal force or load generated thereby during normal operation. It is well known that the rotational speed of the components in the gas turbine engine and the size of the rotor disk and blades impact the potential centrifugal load developed by the rotating assembly. Traditionally, designers of gas turbine engines have balanced many parameters in order to develop a rotor that meets product performance requirements, maintains an acceptable service life, and minimizes catastrophic failure during operation.
Conventional rotor disks are known to fail due to propagating cracks that can develop under relatively high centrifugal loads. Cracks typically form at stress concentrations in the disk such as, for example, undetected inclusions in the disk, or at stress risers such as holes in the disk. In one failure mode, cracks propagate circumferentially around the disk and may result in the rim separating from the web. In another failure mode, cracks propagate in a radial direction through the hub, web, and rim thereby radially splitting the disk and resulting in failure. Rotor disks operate in a hostile environment and must be designed to withstand the stresses created due to centrifugal loading.
With reference to FIG. 1, there is illustrated a prior art conventional rotor disk design for use in a gas turbine engine. Gas turbine engine rotor assembly `a` includes a blade `b` fastened, integrally or through mechanical attachment, to a supporting hub `c`. The supporting hub `c` comprising a thickened rim section `d`, a relatively thin web section `e` and a thickened bore section `f`. The thickened bore section `f` functions to resist the centrifugal force generated by the rotating disk assembly `a`. In the past decade much effort has been expended to increase the reliability, fuel efficiency and performance of gas turbine engines. Most recently designers of gas turbine engines have been working to reduce the weight of rotor assemblies through the incorporation of high specific strength support systems.
High specific strength support systems include organic matrix composites, metal matrix composites, and ceramic matrix composites. With reference to FIG. 2, there is illustrated a metal matrix composite blade ring (bling) that has been actively pursued by gas turbine engine designers. One limitation associated with a circumferentially reinforced metal matrix composite bling design is the transverse (radial) load capability at the outer diameter of the ring. Since a weak bond exists at the fiber/matrix interface, transverse tensile load cannot be transmitted across fibers and must be carried through the matrix only. A circumferentially reinforced metal matrix composite ring has superior load carrying characteristics when loaded at its base since the fibers can transmit compressive transverse load. Further limitations associated with the metal matrix composite bladed ring (bling) relate to it's manufacturability, maintainability, and acquisition cost projections.
Although the prior techniques of producing a reduced weight rotor disk are steps in the right direction, the need for additional improvement still remains. The present invention satisfies this need in a novel and unobvious way.